A new system that may allow people to detect pesticides cheaply and rapidly, combining a paper sensor and an Android program on a smartphone, has been developed by researchers in China and Singapore, according to a new study published in Biosensors and Bioelectronics.

As the potential effects of pesticides on health become clearer, it is increasingly important to be able to detect them in the environment and on foods, but existing gear that purpose is large, expensive, and slow.

Smaller detectors have been developed using paper as a sensor material, but they have not produced strong enough signals for detection. Now researchers at Hefei University of Technology in China and the National University of Singapore have developed a portable smartphone-based detection system using a paper sensor that they say produces signals stronger enough to allow for pesticide detection.

The researchers tested it on thiram, which is used to prevent fungal diseases in seed and crops and an animal repellent to protect fruit trees.

The device uses nanoparticles covered with copper ions that are coated onto paper, causing pesticide molecules to attach to the copper ions. A near-infrared mini-laser shines a light onto the paper, the smartphone detects the absorption spectrum, and an Android app then calculates pesticide concentration, down to 0.1 μM (micromolar) concentration.

The researchers are now developing kits that can multiplex (detect different molecules simultaneously), which would allow for testing food before using it in a meal, for example.

This work was supported by the National Natural Science Foundation of China and the Fundamental Research Funds for the Central Universities.

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Abstract of Smartphone based visual and quantitative assays on upconversional paper sensor

The integration of smartphone with paper sensors recently has been gain increasing attentions because of the achievement of quantitative and rapid analysis. However, smartphone based upconversional paper sensors have been restricted by the lack of effective methods to acquire luminescence signals on test paper. Herein, by the virtue of 3D printing technology, we exploited an auxiliary reusable device, which orderly assembled a 980 nm mini-laser, optical filter and mini-cavity together, for digitally imaging the luminescence variations on test paper and quantitative analyzing pesticide thiram by smartphone. In detail, copper ions decorated NaYF₄:Yb/Tm upconversion nanoparticles were fixed onto filter paper to form test paper, and the blue luminescence on it would be quenched after additions of thiram through luminescence resonance energy transfer mechanism. These variations could be monitored by the smartphone camera, and then the blue channel intensities of obtained colored images were calculated to quantify amounts of thiram through a self-written Android program installed on the smartphone, offering a reliable and accurate detection limit of 0.1 μM for the system. This work provides an initial demonstration of integrating upconversion nanosensors with smartphone digital imaging for point-of-care analysis on a paper-based platform.